Detection apparatus usable in a nuclear reactor, and associated method

ABSTRACT

A detection apparatus includes a resonant electrical circuit supported within an interior of a nuclear fuel rod generates a response pulse in response to an excitation pulse and transmits the response pulse through a cladding of the fuel rod to another location within a reactor in which the fuel rod is housed and without any breach in the cladding. A characteristic of the response pulse is indicative of a condition of the fuel rod. The detection apparatus also includes a transmitter positioned outside the cladding, in the reactor, in the vicinity of the fuel rod and configured to generate the excitation pulse and transmit the excitation pulse through the cladding to the resonant electrical circuit. A receiver is supported within the reactor outside of the cladding and, in response to the response pulse, communicates a signal to an electronic processing apparatus outside of the reactor.

CROSS REFERENCE TO RELATED APPLICATIONS

The instant application claims priority from U.S. Provisional PatentApplication Ser. Nos. 62/691,178 filed Jun. 28, 2018 and 62/596,311filed Dec. 8, 2017, the disclosures of which are incorporated herein byreference.

BACKGROUND 1. Field

The disclosed and claimed concept relates generally to nuclear powerequipment and, more particularly, to a detection apparatus usable with afuel rod and an instrumentation tube of a fuel assembly of a nuclearreactor.

2. Related Art

In many state-of-the-art nuclear reactor systems, in-core sensors areemployed for directly measuring the radioactivity within the core at anumber of axial elevations. Thermocouple sensors are also located atvarious points around the core at an elevation where the coolant exitsthe core to provide a direct measure of coolant outlet temperature atvarious radial locations. These sensors are used to directly measure theradial and axial distribution of power inside the reactor core. Thispower distribution measurement information is used to determine whetherthe reactor is operating within nuclear power distribution limits. Thetypical in-core sensor used to perform this function is a self-powereddetector that produces an electric current that is proportional to theamount of fission occurring around it. This type of sensor is generallydisposed within an instrument thimble within various fuel assembliesaround the core, does not require an outside source of electrical powerto produce the current, is commonly referred to as a self-powereddetector, and is more fully described in U.S. Pat. No. 5,745,538, issuedApr. 28, 1998, and assigned to the Assignee of this invention.

Another type of sensor capable of measuring various parameters of thecore, and which is typically disposed within the instrument thimbles invarious fuel assemblies around the core, is described in U.S. patentapplication Ser. No. 15/417,504, filed Jan. 27, 2017. This type ofsensor employs a transmitter device that includes a self-powered neutrondetector structured to detect neutron flux, a capacitor electricallyconnected in parallel with the neutron detector, a gas discharge tubehaving an input end and an output end, and an antenna electricallyconnected to the output end in series with a resonant circuit. The inputend of the gas discharge tube is electrically connected to thecapacitor. The antenna is structured to emit a signal comprising aseries of pulses representative of the intensity of the neutron fluxmonitored by the self-powered detector. Other core parameters can alsobe monitored by their effects on altering the values of the inductanceand capacitance of the resonant circuit.

Still another in-core sensor, one which does not require signal leads tocommunicate its output out of the reactor, is disclosed in U.S. Pat. No.4,943,683, which describes an anomaly diagnosis system for a nuclearreactor core having an anomaly detecting unit incorporated into a fuelassembly of the nuclear reactor core, and a transmitter-receiverprovided outside the reactor vessel. The transmitter-receiver transmitsa signal wirelessly to the anomaly detecting unit and receives an echosignal generated by the anomaly detecting unit wirelessly. When theanomaly detecting unit detects an anomaly in the nuclear reactor core,such as an anomalous temperature rise in the fuel assembly, the mode ofthe echo signal deviates from a reference signal. Then thetransmitter-receiver detects the deviation of the echo signal from thereference signal and gives an anomaly detection signal to a plantprotection system. The sensor actually monitors coolant temperaturearound the fuel assembly in which it is mounted.

While each of the foregoing sensors directly monitors conditions withinthe core of a nuclear reactor, such sensor have not been withoutlimitation. Improvements thus would be desirable.

SUMMARY

None of the aforementioned sensors directly monitors conditions within anuclear fuel rod in the core during reactor operation. Before advancedfuel cladding materials can be put into commercial use they have to berigorously tested to receive regulatory approval. The existingmethodology for testing advanced fuel cladding materials requires fuelrods to be tested over several fuel cycles and examined at the end ofthe irradiation test. This is a lengthy process that takes several yearsduring which time fuel cladding data is not available. In the existingmethod, critical data is only obtained during the post irradiationexamination activities. What is desired is an in-pile sensor that can beplaced within a fuel rod, endure the hazardous conditions over severalfuel cycles, and does not require penetrations into the cladding of thefuel rod.

This invention achieves the foregoing objective by providing a nuclearfuel rod real-time passive integral detection apparatus with a remoteinductive or magnetic interrogator (also known as pulse induction). Thedetection apparatus includes a resonant electrical circuit configured tobe supported within an interior of a nuclear fuel rod and structured togenerate a generally sinusoidal response pulse in response to anincoming excitation pulse and transmit the response pulse in the form ofa magnetic wave that travels through a cladding of the nuclear fuel rodto another location within a reactor in which the nuclear fuel rod ishoused, wherein a characteristic of the generated pulse is indicative ofa condition of the fuel rod. The detection apparatus also includes atransmitter structured to be positioned outside the cladding, in thereactor, in the vicinity of the fuel rod and configured to generate theexcitation pulse and transmit the excitation pulse through the claddingto the resonant electrical circuit, and a receiver structured to besupported within the reactor outside of the cladding, in the vicinity ofthe nuclear fuel rod, and configured to receive the response pulse and,in response to the response pulse, communicates a signal to anelectronic processing apparatus outside of the reactor.

Preferably, the resonant circuit is supported within a plenum of thenuclear fuel rod. In one such embodiment the characteristic of theresponse pulse is indicative of the center-line fuel pellet temperature.In another such embodiment the characteristic of the response pulse isindicative of fuel pellet elongation. In still another such embodimentthe characteristic of the response pulse is indicative of fuel rodinternal pressure. Furthermore, the characteristic of the response pulsemay be configured to be simultaneously indicative of a plurality ofconditions of the fuel rod.

An additional resonant electrical circuit can also be located in abottom portion of the fuel rod in order to provide measurements at twodifferent axial locations. Preferably, the resonant circuit comprises aplurality of circuit components whose properties such as capacitance andinductance are selected to create a response pulse having a uniquefrequency, which can be interpreted to identify the particular nuclearfuel rod from which the generated pulse emanated.

In addition, the detection apparatus may include a calibration circuitthat is configured to be supported within the interior of the nuclearfuel rod and structured to generate a static calibration signal wheninterrogated by the excitation pulse from the transmitter, which can bereceived by the receiver and used to correct the response pulse receivedby the receiver for any signal change associated with componentdegradation or temperature drift.

Accordingly, an aspect of the disclosed and claimed concept is toprovide an improved detection apparatus usable with a fuel rod fromamong a plurality of fuel rods of a fuel assembly, the fuel rod having acladding that has an interior region, the fuel rod being situated withina nuclear reactor, the detection apparatus being cooperable with anelectronic processing apparatus situated outside of the reactor. Thedetection apparatus can be generally stated as including a transmitterthat is structured to be positioned outside the cladding and inside thenuclear reactor in the vicinity of the fuel rod and structured togenerate an excitation pulse and to transmit the excitation pulsethrough the cladding and into the interior region, an electrical circuitapparatus having a resonant electrical circuit that is structured to besupported within the interior region and to generate a response pulse inresponse to the excitation pulse and to transmit the response pulse inthe form of a magnetic wave that is structured to travel from theinterior region and through the cladding, a characteristic of theresponse pulse being indicative of a condition of the fuel rod, and areceiver structured to be supported within the nuclear reactor outsidethe cladding and in the vicinity of the fuel rod, the receiver beingstructured to receive the response pulse and to communicate to theelectronic processing apparatus an output responsive to the responsepulse.

Another aspect of the disclosed and claimed concept is to provide animproved method of detecting a condition of a fuel rod from among aplurality of fuel rods of a fuel assembly, the fuel rod having acladding that has an interior region, the fuel rod being situated withina nuclear reactor, the detection apparatus being cooperable with anelectronic processing apparatus situated outside of the reactor. Themethod can be generally stated as including employing a detectionapparatus to detect the condition, the detection apparatus having atransmitter that is positioned outside the cladding and inside thenuclear reactor in the vicinity of the fuel rod, an electrical circuitapparatus having a resonant electrical circuit that is supported withinthe interior region, and a receiver that is supported within the nuclearreactor outside the cladding and in the vicinity of the fuel rod. Theemploying can be generally stated as including generating with thetransmitter an excitation pulse and transmitting the excitation pulsethrough the cladding and into the interior region, generating with theelectrical circuit apparatus a response pulse in response to theexcitation pulse and transmitting the response pulse in the form of amagnetic field signal from the interior region and through the cladding,generating the response pulse to have a characteristic that isindicative of the condition of the fuel rod, and receiving the responsepulse on the receiver and communicating to the electronic processingapparatus an output responsive to the response pulse.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the invention can be gained from thefollowing Description when read in conjunction with the accompanyingdrawings in which:

FIG. 1 is a functional schematic of an improved detection apparatus inaccordance with a first embodiment of the disclosed and claimed conceptthat is usable with a fuel rod and an instrument thimble of a nuclearinstallation;

FIG. 2 is a schematic depiction of a nuclear installation having anuclear reactor that includes a fuel assembly that, in turn, includesthe fuel rod and instrument thimble with which the detection apparatusof FIG. 1 is usable;

FIG. 3 is another schematic depiction of the detection apparatus of FIG.1;

FIG. 4 is a partially cut away depiction of a fuel rod within which anelectrical circuit apparatus of the detection apparatus of FIG. 1 issituated;

FIG. 5A is a depiction of a trace of an exemplary response signal thatis output by the electrical circuit apparatus of FIG. 4;

FIG. 5B is an exemplary alternative trace of an alternative responsesignal that is output by the electrical circuit apparatus of FIG. 4;

FIG. 6 is a depiction of another fuel rod, partially cut away, andincluding an electrical circuit apparatus in accordance with a secondembodiment of the disclosed and claimed concept;

FIG. 7 is a graph depicting variation in permeability as a function oftemperature of a ferritic rod of the electrical circuit apparatus ofFIG. 6;

FIG. 8 is a schematic depiction of an electrical circuit apparatus inaccordance with a third embodiment of the disclosed and claimed conceptthat can be used in a fuel rod such as is depicted generally in FIG. 2;

FIG. 9 is a schematic depiction of a fuel rod within which is situatedan electrical circuit apparatus in accordance with a fourth embodimentof the disclosed and claimed concept;

FIG. 10 is a schematic depiction of another fuel rod within which issituated another electrical circuit apparatus in accordance with a fifthembodiment of the disclosed and claimed concept;

FIG. 11 is a schematic depiction of another fuel rod within which issituated another electrical circuit apparatus in accordance with a sixthembodiment of the disclosed and claimed concept;

FIG. 12 is a schematic depiction of another electrical circuit apparatusin accordance with a seventh embodiment of the disclosed and claimedconcept that can be used in a fuel rod such as is depicted generally inFIG. 2; and

FIG. 13 is a schematic depiction of another fuel rod within which issituated another electrical circuit apparatus in accordance with aneighth embodiment of the disclosed and claimed concept.

Similar numerals refer to similar parts throughout the specification.

DESCRIPTION

An improved detection apparatus 4 in accordance with the disclosed andclaimed concept is depicted generally in FIG. 1. The detection apparatus4 is usable with a fuel rod 6 and an instrument thimble 8, such as areincluded in a fuel assembly 10 (FIG. 2) of a nuclear reactor that isdepicted schematically in FIG. 2 at the numeral 12, which signifies acontainment of the nuclear reactor 12.

The detection apparatus 4 is situated within the containment of thenuclear reactor 12, and the detection apparatus 4 is cooperable with anelectronic processing apparatus 16 that is situated external to thecontainment of the nuclear reactor 12. The detection apparatus 4 is thusintended to be situated within the harsh environment situated within theinterior of the containment of the nuclear reactor 12 whereas theelectronic processing apparatus 16 is situated in a mild environmentexternal to the containment of the nuclear reactor 12.

As can be understood from FIG. 1, the electronic processing apparatus 16can be seen as including a transceiver 18 and a signal processor 22. Thetransceiver 18 is connected with a wired connection with aninterrogation apparatus 48 that is situated in the instrument thimble 8.The signal processor 22 includes a processor and storage 24, with thestorage 24 having stored therein a number of routines 28, and thestorage 24 further having stored therein a number of data tables 30. Theroutines 28 are executable on the processor to cause the detectionapparatus 4 to perform various operations, including receiving signalsfrom the transceiver 18 and accessing the data tables 30 in order toretrieve values that correspond with aspect of the signals from thetransceiver 18 that are representative of conditions inside the fuel rod6.

As can further be understood from FIG. 1, the fuel rod 6 can be said toinclude a cladding 32 and to have an interior region 36 situated withinthe cladding 32 and a number of fuel pellets 38 situated within theinterior region 36. As employed herein, the expression “a number of” andvariations thereof shall refer broadly to any non-zero quantity,including a quantity of one. The fuel rod has a plenum 42 in generally avertically upper end of the fuel rod 6.

The detection apparatus 4 can be said to include an electrical circuitapparatus 44 that is supported within the plenum 42 of the fuel rod 6within the interior region 36 thereof. The detection apparatus 4 furtherincludes the interrogation apparatus 48, which can be said to besituated within an interior of the instrument thimble 8. As isschematically depicted in FIG. 1, the electrical circuit apparatus 44 issituated within the interior region 36 and communicates with theinterrogation apparatus 48 without any breaches or other openings beingformed in the cladding 32, thereby advantageously keeping the cladding32 intact and advantageously keeping the fuel pellets 38 fully containedwithin the interior region 36.

As can be further understood from FIG. 1, and as will be set forth ingreater detail below, the electrical circuit apparatus 44 and theinterrogation apparatus 48 communicate wirelessly with one another.Conditions within the interior region 36 of the fuel rod 6 can be saidto include a temperature of the fuel pellets 38, an extent of physicalelongation of the fuel pellets 38, and the ambient pressure within theinterior of the fuel rod 6, by way of example. These three conditionsare directly detectable by the electrical circuit apparatus 44 and arecommunicated through the interrogation apparatus 48 to the electronicprocessing apparatus 16. As will likewise be set forth in greater detailbelow, various embodiments are disclosed wherein the temperature andelongation of the fuel pellets 38 are detected in various ways, andwherein the ambient pressure within the interior region 36 of the fuelrod 6 is detected in various ways. It is understood that theseproperties are not intended to be limiting, and it is also understoodthat other properties potentially can be detectable without departingfrom the spirit of the instant disclosure.

As can be understood from FIG. 3, the electrical circuit apparatus 44can be said to include a resonant electrical circuit 50 that operates asa sensor and that includes a plurality of circuit components thatinclude a capacitor 54 and an inductor 56. The circuit components havevalues or properties, such as the capacitance of the capacitor 54 andthe inductance of the inductor 56, by way of example, which are selectedto impart to the resonant electrical circuit 50 a unique nominalfrequency which, when detected by the interrogation apparatus 48, isusable to identify the particular fuel rod 6 within which the electricalcircuit apparatus 44 is situated.

In this regard, it is understood that a plurality of instances of theelectrical circuit apparatus 44 can be situated in a plurality ofcorresponding fuel rod 6 of the fuel assembly 10. During operation ofthe detection apparatus 4, the interrogation apparatus 48 interrogatesthe electrical circuit apparatus 44 in order to receive a signal fromthe electrical circuit apparatus 44 that can be interpreted as beingindicative of one or more of the properties or conditions within theinterior region 36 of the fuel rod 6, such as temperature and/orelongation of the fuel pellets 38, ambient pressure within the interiorregion 36 of the fuel rod 6, etc., and by way of example. The fuelassembly 10 includes a large number of the fuel rods 6, and a subset ofthe fuel rods 6 of the fuel assembly 10 are envisioned to each have acorresponding electrical circuit apparatus 44 situated therein. When theinterrogation apparatus 48 sends out its interrogation signal, thevarious electrical circuit apparatuses 44 will responsively output asignal that is transmitted through the cladding 32 or the correspondingfuel rod 6 and is received by the interrogation apparatus 48. Thevarious signals from the various electrical circuit apparatuses 44 eachhas a unique nominal frequency that is selected by selecting the variousproperties of the capacitor 54 and the inductor 56, by way of example,of the electrical circuit apparatus 44 in order to provide such asignature frequency. The electric processing apparatus 16 is thus ableto use the frequencies of the various detected signals to determinewhich signal corresponds with which fuel rod 6 of the fuel assembly 10.

As can further be understood from FIG. 3, the electrical circuitapparatus 44 additionally includes a resonant electrical circuit 60 thatis usable as a calibration circuit. That is, the resonant electricalcircuit 50 is usable as a sensor circuit that senses the property orcondition within the interior region 36 of the fuel rod 6, and theresonant electrical circuit 60 is usable as a calibration circuit tocompensate the signal from the resonant electrical circuit 50 forcomponent degradation, temperature drift, and the like. In this regard,the resonant electrical circuit 60 includes a capacitor 62 and aninductor 66 that are selected to have the same material properties asthe capacitor 54 and the inductor 56 of the resonant electrical circuit50. However, and as will be set forth in greater detail below, theresonant electrical circuit 50 is exposed to the condition that is beingmeasured within the interior region 36, such as the temperature and/orelongation of the fuel pellets 38, and/or the ambient pressure withinthe interior region 36, by way of example. The resonant electricalcircuit 60, being usable as a calibration circuit, is generally not soexposed to the condition being measured. Such calibration is provided byemploying a ratiometric analysis such as will be discussed in greaterdetail elsewhere herein.

As can further be understood from FIG. 3, the interrogation apparatus 48can be said to include a transmitter 68 and a receiver 72. Thetransmitter 68 is configured to output an excitation pulse 74 which isin the form of a magnetic field signal that is capable of beingtransmitted through the cladding of the instrument thimble 8 withinwhich the interrogation apparatus 48 is situated and is further capableof being transmitted through the cladding 32 of the fuel rod 6. Theexcitation pulse 74 is thus receivable by the inductor 56 and theinductor 66 of the resonant electrical circuits 50 and 60, respectively,to induce a resonant current in the resonant electrical circuits 50 and60 in a known fashion. The induced currents in the resonant electricalcircuits 50 and 60 result in the outputting of a response pulse 78 fromthe resonant electrical circuit 50 and a response pulse 80 from theresonant electrical circuit 60. The responses pulses 78 and 80 are inthe form of magnetic field signals, which are not merely radio frequencysignals, and which can be transmitted from the electrical circuitapparatus 44 through the cladding 32 and through the cladding of theinstrument thimble 8 and thus be received on the receiver 72.

The excitation pulse 74 is of a generally sinusoidal configuration. Theresponse pulses 78 and 80 are likewise sinusoidal pulses, but they aredecaying sinusoidal signals, and it is noted that FIGS. 5A and 5B depicta pair of traces that are representative of two different responsepulses 78. In this regard, the frequency of the response pulse 78 maycorrelate with one parameters within the fuel rod 6, such astemperature, the peak amplitude of the response pulse 78 may correspondwith another parameter within the fuel rod 6, such as elongation of thefuel pellets 38, and a decay rate of the response pulse rate 78 maycorrelate with yet another parameter within the fuel rod 6, such asambient pressure within the interior region 36. As such, the responsepulse 78 may be correlated with a plurality of parameters or conditionswithin the interior region 36 of the fuel rod 6 within which theelectrical circuit apparatus 44 is situated.

The aforementioned ratiometric analysis of the response pulses 78 and 80typically involves taking a ratio of the response pulse 78 to theresponse pulse 80 or vice versa, in order to eliminate the effects ofcomponent degradation and temperature drift. For instance, the resonantelectrical circuits 50 and 60 may degrade over time thus affecting thesignal that is output therefrom. Likewise, the signals that are outputfrom the resonant electrical circuits 50 and 60 can vary withtemperature of the nuclear reactor 12. In order to compensate for thesefactors, it is assumed that the resonant electrical circuit 50 and theresonant electrical circuit 60 will degrade at substantially the samerate over time. Furthermore, the resonant electrical circuits 50 and 60will be exposed to the same gross, i.e., overall, temperature within theinterior of the nuclear reactor 12. By taking the ratio of the responsepulses 78 and 80, such as the ratio of the frequencies, by way ofexample, and by using the ratio to look up in the data tables 30 acorresponding value for temperature, elongation, and/or pressure, theindividual effects of component degradation and temperature drift in theresonant circuit 50 are eliminated. This is because the ratiometricsignal is independent of component degradation and temperature driftsince the resonant electrical circuits 50 and 60 are assumed to bothexperience the same component degradation and temperature drift.

As is best shown in FIG. 4, the electrical circuit apparatus 44 furtherincludes a elongation transmission apparatus 84 that is situated withinthe interior region 36 of the fuel rod 6. The elongation transmissionapparatus 84 includes a support 86 that is formed of a ceramic materialin the depicted exemplary embodiment and which is abutted against thestack of fuel pellets 38. The support 86 has a receptacle 87 formedtherein, and the elongation transmission apparatus 84 further includesan elongated element that is in the form of a ferritic rod 88 and thatis received in the receptacle 87. The inductor 56 includes a coil 90that is situated about and exterior surface of a tube 92 that is formedof a ceramic material. The tube 92 has an interior 94 within which anend of the ferritic rod 88 opposite the support 86 is receivable.

As the fuel pellets 38 increase in temperature, they thermally expand,thus causing the fuel pellets 38 to push the support 86 and thus theferritic rod 88 in a rightward direction in FIG. 4, and thus to bereceived to a relatively greater extent within the interior 94, whichalters the inductance of the inductor 56. Such an alteration of theinductance of the inductor 56 adjusts the frequency of the resonantelectrical circuit 50, which is detectable when the excitation pulse 74excites an electrical resonance in the resonant electrical circuit 50.The response pulse 78 from the resonant electrical circuit 50 thus has afrequency that is indicative of the extent of elongation of the fuelpellets 38. The response pulses 78 and 80 are received by the receiver72, and the receiver 72 responsively sends a number of signals to theelectronic processing apparatus 16. The electronic processing apparatus16 uses the ratio of the response pulses 78 and 80, or vice versa, toretrieve from the data tables 30 an identity of the fuel rod 6 withinwhich the electrical circuit apparatus 44 is situated, based upon thesignature nominal frequency of the response pulses 78 and 80, andadditionally retrieves from the data tables 30 a value that correspondswith the extent of elongation of the fuel pellets 38 as exemplified bythe response pulse 78. These data can then be sent into a main datamonitoring system of the nuclear reactor 12, by way of example, orelsewhere.

In this regard, it is noted that the calibration circuit represented bythe resonant electrical circuit 60 is not strictly critical for thedetection of the properties or conditions such as fuel elongation,center line fuel temperature, and ambient pressure, within the interiorof the various fuel rods 6. As such, it is understood that thecalibration circuit 60 is optional in nature and is usable in order tosimplify the data gathering operation and to overcome limitationsassociated with component degradation and temperature drift, but thecalibration circuit 60 is not considered to be necessary to theoperation of the detection apparatus 4. As such, it is understood thevarious other types of electrical circuit apparatuses in the variousother embodiments that are described elsewhere herein may or may notinclude a calibration circuit without departing from the spirit of theinstant disclosure. In this regard, it is noted that the calibrationcircuit 60 is described only in terms of the electrical circuitapparatus 44, but it is understood that any of the other embodiments ofthe other electrical circuit apparatuses herein may incorporate such acalibration circuit.

As suggested above, the response pulse 78 is a decaying sine wave thathas properties such as a peak amplitude, a frequency, and a rate ofdecay. FIG. 5A depicts a trace 96A of one such response pulse 78, andFIG. 5B depicts another trace 96B of another such response pulse 78. Itcan be understood from FIGS. 5A and 5B that the trace of FIG. 5A has agreater peak amplitude, a higher frequency (as indicated by the shorterperiod 98A compared with the period 98B in FIG. 5B), and further has ahigher rate of decay than the trace 96B of FIG. 5B. As such, while anyone of temperature, pressure, and elongation can be directly measuredfrom the frequency of either of the traces 96A and 96B, it is understoodthat a plurality of such parameters can be simultaneously derived fromeach such trace 96A and 96B depending upon the configuration of theroutines 28 and the data tables 30, by way of example.

It thus can be said that elongation of the fuel pellets 38 can affectthe inductance value of the inductor 56 by virtue of the relativemovement of the ferritic rod 88 with respect to the coil 90. Thisaffects the frequency of the response pulse 78 that is output by theresonant electrical circuit 50, and which is therefore detectable by theelectronic processing apparatus 16 through the use of the routines 28and the data table 30.

FIG. 6 depicts an improved electrical circuit apparatus 144 inaccordance with a second embodiment of the disclosed and claimedconcept. The electrical circuit apparatus 144 includes a resonantelectrical circuit 150 having a capacitor 154 and an inductor 156, andis thus similar in that fashion to the electrical circuit apparatus 44.However, the electrical circuit apparatus 144 includes a temperaturetransmission apparatus 184 that enables measurement of the center linefuel pellet temperature within the fuel rod 6. Specifically, thetemperature transmission apparatus 184 includes a modified fuel pellet186 that is modified to have a receptacle 187 formed therein. Thetemperature transmission apparatus 184 further includes a tungsten rod189 that is an elongated element and that is received in the receptacle187. While the elongated element 189 is depicted in the exemplaryembodiment described herein as being formed of tungsten, it isunderstood that any of a wide variety of other refractory metals andalloys such as molybdenum and the like can be used in place of tungsten.The temperature transmission apparatus 184 further includes a ferriticrod 188 that is abutted against the tungsten rod 189, it beingunderstood that the tungsten rod 189 is abutted with the modified fuelpellet 186. The inductor 156 includes a coil 190 that is situateddirectly on the ferritic rod 188.

During operation, the heat that is generated by the fuel pellets 38 andthe modified fuel pellet 186 is conducted through the tungsten rod 189and thereafter through the ferritic rod 188, thereby causing thetemperature of the ferritic rod 188 to correspond with the temperatureof the fuel pellets 38 and the modified fuel pellet 186. Thepermeability of the ferritic rod 188 changes as a function oftemperature, and the change in permeability with temperature is depictedin a graph that is shown generally in FIG. 7. A portion of the graph ofFIG. 7 is encircled and demonstrates the temperature that is typicallyseen by the ferritic rod 188 after the heat from the modified fuelpellet 186 is transferred to the ferritic rod 188 by the tungsten rod189 and demonstrates, due to the steepness of the curve at the indicatedlocation in FIG. 7, the correlation between temperature of the ferriticrod 188 and permeability thereof.

The permeability of the ferritic rod 188 which, as noted, varies as afunction of temperature, affects the inductance of the inductor 156 withthe result that the frequency of the response pulse 78 that is output bythe resonant circuit 150 varies directly with the permeability of theferritic rod 188 and thus with the temperature of the fuel pellets 38and the modified fuel pellet 186. As such, the temperature of the fuelpellets 38 and the modified fuel pellet 186 can be measured by detectingthe response pulse 78 that is output by the resonant electrical circuit150 through the use of the routines 28 and the retrieval from the datatables 30 of a temperature that corresponds with the detected frequencyof the response pulse 78.

An improved electrical circuit apparatus 244 in accordance with a thirdembodiment of the disclosed and claimed concept is depicted in FIG. 8and is usable in a fuel rod in a fashion similar to the electricalcircuit apparatus 44. The electrical circuit apparatus 244 is receivablein the interior region 36 of the fuel rod 6 and includes a resonantelectrical circuit 250 and a temperature transmission apparatus 284 thatdetect the temperature of a set of modified fuel pellets 286. Themodified fuel pellets 286 each have a receptacle 287 formed therein. Thetemperature transmission apparatus 284 includes an amount of liquidmetal 291 that is liquid during operation of the nuclear reactor 12. Thetemperature transmission apparatus 284 further includes a ferritic rod288 that is engaged with the liquid metal 291 and is buoyantly floatedthereon and is receivable in the interior of a coil 290 of an inductor256 of the resonant electrical circuit 250. The liquid metal 291 expandsand contracts with temperature increases and decreases, respectively, ofthe modified fuel pellets 286. The position of the ferritic rod 288 withrespect to the coil 290 is thus directly dependent upon the centerlinetemperature of the modified fuel pellets 286. Such position of theferritic rod 288 with respect to the coil 290 affects the inductance ofthe inductor 256 and therefore correspondingly affects the frequency ofthe resonant electrical circuit 250. The response pulse 78 that isgenerated by the resonant electrical circuit 250 thus is receivable bythe receiver 72 and is communicated to the electronic processingapparatus 16, and the routines 28 and the data tables 30 are employed todetermine a corresponding temperature of the modified fuel pellets 286and thus of the corresponding fuel rod 6.

FIG. 9 depicts an improved electrical circuit apparatus 344 inaccordance with a fourth embodiment of the disclosed and claimedconcept. The electrical circuit apparatus 344 is usable inside a fuelrod 6 and includes a resonant electrical circuit 350 and a pressuretransmission apparatus 385. The pressure transmission apparatus 385 isconfigured to enable measurement of the ambient pressure within theinterior of the fuel rod 6 and includes a support 386 that abuts thestack of fuel pellets 338. The pressure transmission apparatus 385further includes a ferritic rod 388 and a vessel in the form of abellows 393 having a hollow cavity 395 and further having a plurality ofcorrugations 396 formed therein. The hollow cavity 395 is open and istherefore in fluid communication with the interior region of the fuelrod 6. Moreover, an end of the bellows 393 opposite a ferritic rod 388is affixed to the support 386.

The resonant electrical circuit 350 includes a capacitor 354 and furtherincludes an inductor 356 having a coil 390 that is formed about theexterior of a hollow tube 392 having an interior 394 within which aferritic rod 388 is receivable. The bellows 393 and the ferritic rod 388are movably received on a support 386 and are biased by a spring in adirection generally toward the fuel pellets 338.

As is understood in the relevant art, as the nuclear reactor 12 is inoperation, fission gases are produced that include one or more noblegases. Such fission gases increase the ambient pressure within theinterior region of the fuel rod 6. Since the hollow cavity 395 is influid communication with the interior region of the fuel rod 6, theincreased pressure in the interior region 36 bears upon bellows 393within the hollow cavity 395 and causes the bellows 393 to expandaxially, thereby moving the ferritic rod 388 with respect to the coil390 and thereby affecting the inductance of the inductor 356. Anincrease in ambient pressure within the interior region 36 of the fuelrod 6 thus expands the bellows 393, thereby resulting in an incrementalfurther reception of the ferritic rod 388 into the coil 390, whichresults in a corresponding change in inductance of the inductor 356.

The corresponding change in inductance of the inductor 356 affects in apredictable fashion the frequency of the resonant electrical circuit 350and thus likewise affects the frequency of the response pulse 78 that isoutput by the resonant electrical circuit 350. As a result, when theresponse pulse 78 from the resonant electrical circuit 350 is receivedby the receiver 72 and is communicated to the electronic processingapparatus 16, the routines 28 and the data tables 30 are employed toobtain a corresponding value for the ambient pressure within theinterior region 36 of the fuel rod 6. Such value for the ambientpressure can then be communicated to an enterprise data system of thenuclear reactor 12.

An improved electrical circuit apparatus 444 in accordance with a fifthembodiment of the disclosed and claimed concept is depicted generally inFIG. 10. The electrical circuit apparatus 444 is situated within aninterior region 436 of a fuel rod 6 and includes a resonant electricalcircuit 450 that includes a capacitor and an inductor 456.

The electrical circuit apparatus 444 further includes a pressuretransmission apparatus 485 that includes a vessel in the form of aBourdon tube 493 which, in the depicted exemplary embodiment, includes ahollow tube that is formed in a helical shape. The hollow tube of theBourdon tube 493 forms a hollow cavity 495, except that an inlet 497 isformed in an end of the Bourdon tube 493 and thus permits fluidcommunication with the interior of the Bourdon tube 493. Morespecifically, the electrical circuit apparatus 444 further includes asupport 486 in the form of a seal that extends between the edges of theBourdon tube 493 adjacent the inlet 497 and extends to an interiorsurface of the interior region 436 of the fuel rod 6. The support 486thus divides the interior region 436 into a main portion 481 withinwhich a number of fuel pellets 438 are situated and a sub-region 483within which the Bourdon tube 493 and the inductor 456 are situated. TheBourdon tube 493 is also supported on the support 486. The support 486resists fluid communication between the main portion 481 and thesub-region 483, except for the inlet 497 which permits fluidcommunication between the interior of the Bourdon tube 493 and the mainportion 481.

The pressure transmission apparatus 485 further includes a ferritic rod488 that is situated on the Bourdon tube 493 at an end thereof oppositethe inlet 497. The inductor 456 includes a coil 490, and movement of theferritic rod 488 in relation to the coil 490 changes the inductance ofthe inductor 456 such that the frequency of the response pulse 78 thatis generated by the electrical circuit apparatus 444 changescorresponding to the ambient pressure within the main portion 481 of theinterior region 436. More specifically, as fission gases accumulate inthe main portion 481 of the interior region 436, the ambient pressurewithin the main portion 481 increases, as does the ambient pressurewithin the hollow cavity 495 of the Bourdon tube 493. Since thesub-region 483 does not experience the increased ambient pressure thatis experienced by the main portion 481, and increase in the ambientpressure within the hollow cavity 495 of the Bourdon tube 493 results inexpansion of the Bourdon tube 493 and resultant movement of the ferriticrod 488 in the direction of the arrow 499 with respect to the coil 490.This results in a corresponding change in the frequency of the responsepulse 78 that is generated by the electrical circuit apparatus 444.

It thus can be seen that changes in ambient pressure within the mainportion 481 of the interior region 436 result in a change in inductanceof the inductor 456 and a corresponding change in the nominal frequencyof the resonant electrical circuit 450 and a resultant change in thefrequency of the response pulse 78 that is generated by the electricalcircuit apparatus 444. When such response pulse 78 is received by thereceiver 72, a corresponding signal is communicated to the electronicprocessing equipment 16, and the routines 28 and the data tables 30 areused to obtain a corresponding value for the ambient pressure within theinterior region 436 for output as desired.

An improved electrical circuit apparatus 544 in accordance with a sixthembodiment of the disclosed and claimed concept is depicted generally inFIG. 11. The electrical circuit apparatus 544 is similar to theelectrical circuit apparatus 444 in that a Bourdon tube 593 is employedas a vessel having a hollow cavity 595. In the electrical circuitapparatus 544, however, the Bourdon tube 593 includes a plug 597 at anend thereof opposite a ferritic rod 588 such that the hollow cavity 595of the Bourdon tube is not in fluid communication with the interiorregion 536 of the fuel rod 6, and an increase in ambient pressure withinthe interior region 536 causes the Bourdon tube 593 to contract. TheBourdon tube 493 is supported on a support 586 in the vicinity of theplug 597, and a contraction of the Bourdon tube 493 due to increasedambient pressure within the interior region 536 thus moves the ferriticrod 588 in the direction of the arrow 599 with respect to the coil 590.

The electrical circuit apparatus 544 includes a resonant electricalcircuit 550 having a capacitor and an inductor 556, and movement of theferritic rod 588 with respect to the coil 590 of the inductor 556changes the inductance of the inductor 556 and thus changes the nominalfrequency of the resonant electrical circuit 550. The electrical circuitapparatus 544 thus includes a pressure transmission apparatus 585 thatis similar to the pressure transmission apparatus 485, except that thepressure transmission apparatus 585 includes a Bourdon tube 593 whosehollow cavity 595 is not in fluid communication with the interior region536 and thus contracts in the presence of an increased ambient pressurewithin the interior region 536.

An improved electrical circuit apparatus 644 in accordance with aseventh embodiment of the disclosed and claimed concept includes aresonant electrical circuit 650 having a capacitor 654 and an inductor.The capacitor 654 includes a pair of plates 652A and 652B that areseparated by a dielectric material 653. The electrical circuit apparatus644 is receivable within the interior region 36 of a fuel rod 6 in orderto output a response pulse 78 whose frequency is adjusted responsive toa change in ambient pressure within the interior region 36 of the fuelrod 6.

More specifically, the dielectric 653 is hygroscopic in nature and isconfigured to absorb at least some of the fission gases that aregenerated during operation of the nuclear reactor 12. Such absorption ofthe fission gases by the dielectric 653 changes the dielectric constantof the dielectric 653, which adjusts the capacitance of the capacitor654, with a corresponding effect on the frequency of the response pulse78 that is generated by the resonant electrical circuit 650. As such, achange in the ambient pressure within the interior region 36 of the fuelrod 6 correspondingly affects the capacitance of the capacitor 654 andthus likewise correspondingly affects the frequency of the responsepulse 78 that is generated by the resonant electrical circuit 650. Whenthe response pulse 78 is received by the receiver 72, the receiver 72responsively provides to the electronic processing apparatus 16 a signalwhich is used by the routines 28 in conjunction with the data tables 30to obtain and output a value for the ambient pressure within theinterior region 36 of the fuel rod 6 within which the electrical circuitapparatus 644 is situated.

An electrical circuit apparatus 744 in accordance with an eighthembodiment of the disclosed and claimed concept is depicted generally inFIG. 13 as being situated within an interior region 736 of a fuel rod 6.The electrical circuit apparatus includes a resonant electrical circuit750 that includes a capacitor 754 and an inductor 756.

The electrical circuit apparatus 744 includes a pressure transmissionapparatus 785 that includes a support 786 upon which the capacitor 756is situated in a stationary fashion and further includes a flexible seal782. More specifically, the capacitor 754 includes a pair of plates 752Aand 752B with a dielectric material 753 interposed therebetween. Theplate 752A is situated on the support 786, and the flexible seal extendsbetween the plate 752B and an interior surface of the fuel rod 6 todivide the interior region 736 into a main portion 781 within which anumber of fuel pellets 738 are situated and a sub-region 783 withinwhich the inductor 756, the plate 752A, the support 786, and thedielectric 753 are situated. The support 786 is rigid but has a numberof openings formed therein such that an increase or decrease in theambient pressure within the main portion 781 will result in movement ofthe flexible seal 782 with respect to the support 786. The flexible seal782 thus resists fluid communication between the main portion 781, whichis the location where the fission gases are generated, and thesub-region 783.

When the main portion 781 experiences a change in the ambient pressurewithin the main portion 781, this causes the flexible seal 782 and theplate 752B to move with respect to the plate 752A which, being situatedon the support 786, remains stationary. The dielectric material 753 isconfigured to be at least partially flexible in response to movement ofthe plate 752B with respect to the plate 752A. However, such movement ofthe plate 752B with respect to the plate 752A results in a change in thecapacitance of the capacitor 754. This results in a corresponding changein the frequency of the response pulse 78 that is generated by theresonant electrical circuit 750 as a result of a change in the ambientpressure within the main portion 781. It thus can be understood that achange in ambient pressure within the main portion 781 of the interiorregion 736 correspondingly changes the frequency of the response pulse78 that is received by the receiver 72 and which resultantlycommunicates a signal to the electronic processing apparatus 16. Theelectronic processing apparatus 16 then employs its routines 28 and itsdata tables 30 to determine a pressure value that corresponds with thefrequency of the response pulse 78 and which is indicative of theambient pressure within the main portion 781 of the interior region 736.

It thus can be seen that various electrical circuit apparatuses areprovided that are able to directly measure parameters such as ambientpressure, centerline fuel pellet temperature, and fuel pellet elongationwithin the various fuel rods 6 of the fuel assembly 10. As noted, any ofthe electrical circuit apparatuses can include the calibration circuitthat is usable to compensate for component degradation and temperaturedrift. In addition to the direct measurement of the parameters such ascenterline fuel pellet temperature, fuel pellet elongation, and ambientpressure within the interior region of the fuel rods 6, it is reiteratedthat the response pulse 78 in certain circumstances can be analyzed interms of its peak amplitude, frequency, and rate of decay in order toindirectly and simultaneously indicate a plurality the same parametersof the fuel rods 6. Other variations will be apparent.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular embodiments disclosed are meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the appended claims and any and all equivalents thereof.

What is claimed is:
 1. A detection apparatus usable with a fuel rod fromamong a plurality of fuel rods of a fuel assembly, the fuel rod having acladding that has an interior region, the fuel rod being situated withina nuclear reactor, the detection apparatus being cooperable with anelectronic processing apparatus situated outside of the reactor, thedetection apparatus comprising: a transmitter that is structured to bepositioned outside the cladding and inside the nuclear reactor in thevicinity of the fuel rod and structured to generate an excitation pulseand to transmit the excitation pulse through the cladding and into theinterior region; an electrical circuit apparatus having a resonantelectrical circuit that is structured to be supported within theinterior region and to generate a response pulse in response to theexcitation pulse and to transmit the response pulse in the form of amagnetic field signal that is structured to travel from the interiorregion and through the cladding, a characteristic of the response pulsebeing indicative of a condition of the fuel rod; and a receiverstructured to be supported within the nuclear reactor outside thecladding and in the vicinity of the fuel rod, the receiver beingstructured to receive the response pulse and to communicate to theelectronic processing apparatus an output responsive to the responsepulse.
 2. The detection apparatus of claim 1 wherein the resonantelectrical circuit is supported within a plenum of the nuclear fuel rod.3. The detection apparatus of claim 2 wherein the characteristic of theresponse pulse is indicative of a center-line fuel pellet temperature.4. The detection apparatus of claim 2 wherein the characteristic of theresponse pulse is indicative of a fuel pellet elongation.
 5. Thedetection apparatus of claim 2 wherein the characteristic of theresponse pulse is indicative of a pressure in the interior region. 6.The detection apparatus of claim 2 wherein the characteristic of theresponse pulse is indicative of a plurality of conditions of the fuelrod.
 7. The detection apparatus of claim 1 wherein the resonantelectrical circuit comprises a plurality of circuit components whosevalues are selected to cause the response pulse to have a uniquefrequency that is usable to identify the fuel rod from which theresponse pulse emanated.
 8. The detection apparatus of claim 1 whereinthe electrical circuit apparatus further comprises a calibration circuitthat is configured to be supported within the interior region and thatis structured to generate a calibration signal in response to theexcitation pulse and to transmit the calibration signal in the form ofanother magnetic field signal that is structured to travel from theinterior region and through the cladding, the another magnetic fieldsignal being receivable by the receiver and usable to correct theresponse pulse received by the receiver for any signal change associatedwith component degradation or temperature drift.
 9. The detectionapparatus of claim 1 wherein the resonant electrical circuit comprises aplurality of circuit components that comprise a capacitor, the capacitorhaving a capacitance which is structured to vary in response to thecondition of the fuel rod and which, responsive to a change in thecondition, is structured to cause the response pulse to have a frequencythat varies with the condition.
 10. The detection apparatus of claim 9wherein the capacitor comprises a movable plate and a stationary plate,the movable plate being structured to move with respect to thestationary plate responsive to a change in an ambient pressure withinthe interior region to alter the capacitance and to resultantly causethe response pulse to have a frequency that varies with the ambientpressure.
 11. The detection apparatus of claim 1 wherein the resonantelectrical circuit comprises a plurality of circuit components thatcomprise an inductor having a coil, the inductor having a inductancewhich is structured to vary in response to the condition of the fuel rodand which, responsive to a change in the condition, is structured tocause the response pulse to have a frequency that varies with thecondition.
 12. The detection apparatus of claim 11 wherein the fuel rodhas a number of fuel pellets situated within the interior region,wherein the condition is a center-line fuel pellet temperature of thefuel rod, and wherein the electrical circuit apparatus further comprisesa temperature transmission apparatus comprising an element that iselongated and that is formed at least in part of a ferromagneticmaterial, at least a portion of the element being receivable in thecoil, the at least portion of the element that is receivable in the coilvarying with the condition to cause the inductance to vary in responseto the change in the condition.
 13. The detection apparatus of claim 12wherein the temperature transmission apparatus further comprises anamount of metal, the element being engaged with the amount of metal, theamount of metal being structured to undergo thermal expansion andcontraction as a function of an increase and a decrease, respectively,in the center-line fuel pellet temperature, the element being structuredto be moved relative to the coil by the amount of metal undergoingthermal expansion and contraction to thereby cause the inductance tovary in response to the change in the condition.
 14. The detectionapparatus of claim 13 wherein the amount of metal is in a liquid stateduring operation of the nuclear reactor, wherein the element is floatedon the amount of metal, and wherein the element is structured to bebuoyantly moved relative to the coil by the amount of metal undergoingthermal expansion and contraction.
 15. The detection apparatus of claim11 wherein the condition is an ambient pressure within the interiorregion, and wherein the electrical circuit apparatus further comprises apressure indication apparatus comprising an element that is elongatedand that is formed at least in part of a ferromagnetic material, atleast a portion of the element being receivable in the coil, the atleast portion of the element that is receivable in the coil varying withthe condition to cause the inductance to vary in response to the changein the condition.
 16. The detection apparatus of claim 15 wherein thepressure indication apparatus further comprises a vessel having a hollowcavity that is sealed to resist fluid communication with the interiorregion, the vessel being structured to be supported within the interiorregion and being structured to undergo contraction and expansion inresponse to an increase and a decrease, respectively, in the ambientpressure within the interior region, the element being situated on thevessel being structured to be moved relative to the coil by the vesselundergoing contraction and expansion to thereby cause the inductance tovary in response to the change in the condition.
 17. The detectionapparatus of claim 16 wherein the vessel is a bellows having a number ofcorrugations formed therein.
 18. A method of detecting a condition of afuel rod from among a plurality of fuel rods of a fuel assembly, thefuel rod having a cladding that has an interior region, the fuel rodbeing situated within a nuclear reactor, comprising: employing adetection apparatus to detect the condition, the detection apparatusbeing cooperable with an electronic processing apparatus situatedoutside of the nuclear reactor, the detection apparatus having atransmitter that is positioned outside the cladding and inside thenuclear reactor in the vicinity of the fuel rod, an electrical circuitapparatus having a resonant electrical circuit that is supported withinthe interior region, and a receiver that is supported within the nuclearreactor outside the cladding and in the vicinity of the fuel rod, theemploying comprising: generating with the transmitter an excitationpulse and transmitting the excitation pulse through the cladding andinto the interior region; generating with the electrical circuitapparatus a response pulse in response to the excitation pulse andtransmitting the response pulse in the form of a magnetic field signalfrom the interior region and through the cladding; generating theresponse pulse to have a characteristic that is indicative of thecondition of the fuel rod; and receiving the response pulse on thereceiver and communicating to the electronic processing apparatus anoutput responsive to the response pulse.
 19. The method of claim 18,wherein the electrical circuit apparatus further has a calibrationcircuit that is supported within the interior region, and furthercomprising: generating with the calibration circuit a calibration signalin response to the excitation pulse and transmitting the calibrationsignal in the form of another magnetic field signal from the interiorregion and through the cladding; receiving the another magnetic fieldsignal on the receiver; and employing the another magnetic field signalreceived on the receiver to correct the response pulse received by thereceiver for any signal change associated with component degradation ortemperature drift.
 20. The method of claim 19, wherein the employing ofthe another magnetic field signal received on the receiver comprises:employing the characteristic of the response pulse and anothercharacteristic of the calibration signal to determine a ratio; andemploying the ratio to retrieve from a storage a corresponding value forthe condition.